Textured release paper

ABSTRACT

A TEXTURED RELEASE PAPER IS MADE BY FIRST COATING A BASE PAPER WITH A MINERAL PIGMENT COATING HAVING A SMOOTH SURFACE, THEN APPLYING AN ALCOHOLI SOLUTION OF A POLYAMIDE WHICH FORMS A TEXTURED SURFACE UPON DRYING AND CURING. POLYVINYL CHLORIDE PLASTISOLS ARE APPLIED TO THE RELEASE PAPER, FRIED AND CURED, AND WHEN STRIPPED OFF AS SELF-SUPPORTING FILMS EXHIBIT THE SAME EMBOSSED TEXTURE OF THE POLYAMIDE SURFACE. THE RELEASE COATING MAY CONTAIN A THERMOSETTING RESIN WHICH PROVIDES HARDNESS AND SOLVENT RESISTANCE TO THE RELEASE COATING.

United States Patent O 3,667,994 TEXTURED RELEASE PAPER Franklin J. Ward, South Portland, Maine, assignor to Scott Paper Company, Delaware County, Pa. No Drawing. Filed July 24, 1970, Ser. No. 58,175 Int. Cl. B32b 29/00; B44d 1/14 US. Cl. 117--76 P 4 Claims ABSTRACT OF THE DISCLOSURE A textured release paper is made by first coating a base paper with a mineral pigment coating having a smooth surface, then applying an alcoholic solution of a polyamide which forms a textured surface upon drying and curing. Polyvinyl chloride plastisols are applied to the release paper, dried and cured, and when stripped off as self-supporting films exhibit the same embossed texture of the polyamide surface. The release coating may contain a thermosetting resin which provides hardness and solvent resistance to the release coating.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to coatings for paper and related fibrous substrates. More specifically, it relates to coatings which are generally classified in the art as release coatings and which are characterized by their ability to separate intact from a surface which is normally adherent.

History of the prior art In a process for producing films or sheets of thermoplastic material, such as vinyl resins, the material in a flowable form, usually a plastisol, is deposited or cast on the supporting surface, heated to consolidate the thermoplastic material into a continuous self-supporting film, cooled and stripped from the support. A web of paper or equivalent flexible material having a layer of a release coating on its surface is typically used for supporting or carrying the film of thermoplastic material during the process of its consolidation. A release coating is one from which the cold, consolidated film will readily part without being marred or distorted during separation.

The release paper provides a surface against which the thermoplastic material forms and from which it will readily release and imparts to the surface of the material the quality of finish of the release surface. When a textured surface is desired on the surface of the thermoplastic sheet material, the release paper is provided with an embossed surface, generally by mechanically embossing the paper prior to application of the release coating. Mechanical embossing serves this purpose adequately so long as a relatively coarse texture is desired. If the embossure pattern is made very fine, however, there is a tendency for the release coating to fill the depressions in the paper and thus create a smooth surface or for the non-uniformity of the paper surface to mask the embossing.

SUMMARY OF THE INVENTION In accordance with the present invention, when an alcoholic solution of a polyamide resin is included in a release coating, the coating upon drying exhibits an embossed effect. Furthermore, the coarseness of the apparent embossure is inversely proportional to coating weight thus a light-weight coating will produce a very fine embossed pattern, while a heavier coating weight produces a coarser embossed effect.

3,667,994 Patented June 6, 1972 DETAILED DESCRIPTION The release coating formulation of the present invention is applied to a suitable base paper or substrate. The principal requirement for the substrate is that it have a smooth surface which resists the penetration of the release coating into the substrate. In the case of a cellulosic fibrous substrate such as paper, this requirement is typically met by providing the paper with a coating, which comprises mineral pigment, e.g. clay, and an adhesive or binder. In preferred embodiment, the mineral coating comprises a first coating of super-calendered mineral pigment in a natural binder and a second mineral coating applied by a cast coating process.

The polyamide solution employed in the present invention is obtained by dissolving a polyamide resin in a lower alcohol, which may optionally contain a small amount of water. The concentration of the solution is in the range of 525%, and preferably 10 to 20%. Suitable commercially available polyamides include Du Ponts Elvamide 6062 and BASFs (Badische Anilin und Soda Fabrick) Ultramide 6A and Ultramide 1C. By way of illustration, the polyamide of Ultramide 6A is a copolymer of adipic acid, hexamethylene diamine and caprolactam. These polyamides dissolve in lower alcohols and in alcoholic water solutions at elevated temperatures.

To provide hardness and solvent resistance to the release coating, a thermosetting resin is included in the formulation. Suitable examples include amine-formaldehyde resins, phenolics, and epoxy resins. A preferred example is an aqueous solution of melamine formaldehyde resin. To enhance the release properties so that the paper can be used for casting polyurethane films, a silicone may be added.

The principles, features, and advantages of the invention will be further understood upon a consideration of the following specific examples:

EXAMPLE I A sheet of paper having a basis weight of gms./ square meter was made from a moderately beaten furnish of about equal quantities of bleached softwood and hardwood fibers containing a small quantity of clay filler and a chemical size to impart water repellence. This bodystock was then coated on both sides in a conventional manner by means of a roll coater with a composition comprising a mineral pigment and an adhesive, dried and super-calendered. Thereafter a second, or intermediate, coating was applied to one side of the web also in a conventional manner and also using a mineral-pigmentand-adhesive type of coating. This latter coating, however, was dried and glossed by casting the still somewhat wet coating against a heated, highly polished metal drum so that the surface of the coating assumed the smooth, glossy surface of the casting drum.

To this cast-coated side, a release coating of the following composition was applied:

Component: Parts by weight Polyamide, Du Ponts Elvamide 6062 25 Ethanol Water in an amount sufficient to produce a solids content of 10% To the cast-coated side of paper as prepared in Example I was applied a release coating formulation comprising the following:

Parts of component Component: by weight Ethanolic solution of polyamide, by wt.

of Du Ponts Elvarnide 6062 50 Aqueous solution of melamine-formaldehyde resin, 80% resin by wt. (American Cyanamids Aerotex M-3) 1.875 Aqueous solution of NH Cl, 10% conc. 0.5 Ethanol 50 The total solids content of the above formulation was 6.42%. This coating composition was applied to sheets of the cast-coated paper by means of various Bird bars to produce different coating weights. The coatings were cured at 190 C. for l to 1 /2 minutes using a forced hot air heater. A coating weight, dry basis, of about 1.10 gms./square meter produced a smooth surface; a coating weight of 3.75 gms./square meter produced a very fine texture; a coating weight of 12.0 gms./square meter produced a fine pattern suggestive of top grain cowhide finish; and a coating weight of 22 gms./ square meter produced a moderately coarse texture somewhat typical of mechanically embossed patterns.

Polyvinyl chloride plastisols were applied to each of these latter four samples, and dried and cured as described in Example I. In all cases, when the plastisols were stripped oil as self-supporting films, they exhibited the same embossed texture of the polyamide surface on which they were cast.

Thus, it is seen that the present invention provides a release paper having the texture of an embossed sheet, without the necessity of mechanically embossing the paper. The method of the invention is particularly advantageous for producing very fine embossure patterns because the coating compensates for non-uniformities in the paper surface and at the same time produces the desired texture, since the degree of the apparent embossure is controlled by selecting the proper coating weight.

What is claimed is:

1. A textured release paper which comprises a base paper, a mineral pigment coating on at least one side of the paper having a smooth surface which resists the penetration of the release coating into the base paper, and a release coating overlying the pigment coating, comprising in major proportion an alcohol-soluble polyamide and having a textured surface formed by drying and curing of an alcoholic solution of said polyamide.

2. The paper according to claim 1 wherein the release coating further comprises a thermosetting resin in an amount suflicient to provide hardness and solvent resistance to the release coating.

3. The paper according to claim 2 wherein the thermosetting resin is an amine-formaldehyde resin.

4. The paper according to claim 3 wherein the resin is a melamine-formaldehyde resin.

References Cited UNITED STATES PATENTS 2,882,186 4/1959 Schonberg et al. 117--161 P 3,359,127 12/ 1967 Meyer et a1 l1716l PX 3,454,419 7/1969 Smith et al. l17-76 P 3,518,103 6/1970 Visnovsky 11776 PX 3,493,419 2/1970 Jones et al. 117-76 P 3,480,466 11/1969 Benson et al. 117-76 P WILLIAM D. MARTIN, Primary Examiner R. HVSACK, Assistant Examiner US. Cl. X.R. 

